Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 250409
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1209 AM EDT SAT APR 25 2015


.AVIATION...

AREA OF SHOWERS CONTINUES TO STRUGGLE WITH VERY DRY AIR IN PLACE
BELOW 10KFT OR SO. EVEN SO...SOME MOISTURE IS MAKING IT TO THE
GROUND TO THE SOUTHWEST OF THE TERMINALS LATE THIS EVENING. FGEN
WILL PERSIST OVERNIGHT AND UPSTREAM RADAR RETURNS SUGGEST THERE MAY
BE ENOUGH MOISTURE TO BRING A PERIOD OF -SHRAS/SPRINKLES INTO THE
INTERSTATE 94 TAFS OVERNIGHT. CONDITIONS SHOULD REMAIN VFR. SHRAS
WILL FOCUS GRADUALLY SOUTH ON SATURDAY AND WILL JUST MAINTAIN A MID
BKN-OVC DECK ATTM WHICH WILL SCATTER OUT LATE IN THE FORECAST AS
EAST TO NORTHEAST FLOW BACKS TO THE NORTH SATURDAY NIGHT.

FOR DTW...EXPANDING PRECIPITATION SHIELD ASSOCIATED WITH SHORTWAVE
TO THE WEST WILL MOST LIKELY BRING A PERIOD OF -SHRAS OVERNIGHT. VFR
CONDITIONS SHOULD PREVAIL AND CIGS WILL MOST LIKELY REMAIN ABOVE
5KFT AND VSBYS SHOULD NOT BE RESTRICTED MUCH GIVEN THE CURRENT LEVEL
OF DRY AIR IN THE LOWER ATMOSPHERE.

//DTW THRESHOLD PROBABILITIES...

* NONE.

&&

.PREV DISCUSSION...ISSUED 347 PM EDT FRI APR 24 2015

SHORT TERM...TONIGHT

THE TOP OF THE UPPER LEVEL RIDGE SEEN ON WATER VAPOR/SATELLITE
IMAGERY MAKING A RUN TOWARD CHICAGO LOOKS TO BE EXTENDING TO THE
SOUTHERN MICHIGAN BORDER TONIGHT...WITH SHARP MOISTURE GRADIENT
KNOCKING ON OUR DOOR. MEANWHILE...AT THE SURFACE...TWO AREAS OF LOW
PRESSURE OVER THE PLAINS...WITH THE NORTHERN PLAINS LOW OVER SOUTH
DAKOTA GIVING WAY TO THE LOW FARTHER SOUTH OVER NEBRASKA. OVER
SOUTHEAST MICHIGAN...SURFACE HIGH PRESSURE (1018 MB) CONTINUES TO
HOLD...WITH SUNNY SKIES THIS AFTERNOON...HAVING ALLOWED TEMPS TO
REACH INTO THE 50S ACROSS MOST LOCATIONS. AIRMASS REMAINS VERY DRY
AS INDICATED BY THE SURFACE DEW PTS MOSTLY IN THE UPPER TEENS. MODEL
CONSENSUS IS FOR MODEST WARM ADVECTION AND MOISTURE ADVECTION TO
SUPPORT MID CLOUDS TONIGHT...AND FAVOR MORE OF A MOSTLY CLOUDY
FORECAST FOR MOST LOCATIONS...AND SUBSEQUENTLY ADDED A DEGREE OR TWO
TO THE MINS. A QUICK DROP EARLY THIS EVENING IS EXPECTED OVER THE
THUMB REGION TO ALLOW TEMPS TO SNEAK INTO THE UPPER 20S BEFORE
MID/HIGH CLOUDS INCREASE...WITH 30S ELSEWHERE.

VARIOUS MODELS...INCLUDING HIGH RESOLUTION SHORT TERM MODELS
ADVERTISING ENHANCED FGEN BAND(S) AND SUBSEQUENT NARROW LINE OF
SHOWERS ALIGNED ALONG THE 1000-500 MB THICKNESSES FIELDS SLIPPING
INTO SOUTHERN LOWER MICHIGAN. UNTIL THERE IS OVERWHELMING UPSTREAM
RADAR EVIDENCE...SUPPORTED BY GROUND TRUTH...PREFERENCE IS FOR THE
LOW LEVEL DRY AIRMASS TO HOLD OVER THE CWA...WITH MOST LIKELY JUST
VIRGA AROUND. WILL CARRY A LOW CHANCE POP ACROSS THE FAR SOUTHWEST
(LENAWEE COUNTY) WHERE THE DEEPER MOISTURE WILL ATTEMPT TO MOVE IN
BY MORNING.

LONG TERM...SATURDAY THROUGH NEXT FRIDAY

UPPER WAVE EJECTING OUT OF NEW MEXICO WILL LIFT NORTHEAST TONIGHT
AND SATURDAY...TRACKING ACROSS THE OHIO VALLEY. THIS FEATURE WILL
WEAKEN AS IT MOVES TOWARDS THE AREA...AS IT LOSES RIGHT ENTRANCE
REGION FORCING NOW SUPPORTING IT AND MOVES INTO AN AREA OF MORE
CONFLUENT FLOW ALOFT. THE APPROACHING WAVE WILL BE GUIDED TO OUR
SOUTH BY SHORTWAVE ENERGY DROPPING INTO ONTARIO/QUEBEC...AS IT
PIVOTS AROUND THE BACKSIDE OF A LARGE UPPER LOW OFF EAST COAST...THE
SAME LOW THAT RESIDED OVER THE GREAT LAKES JUST A FEW DAYS AGO.

LOW-LEVEL FORCING FROM THE APPROACHING WAVE LOOKS TO REMAIN TO OUR
SOUTH PER LATEST GUIDANCE PACKAGE...WITH JUST MID-LEVEL DEFORMATION
AND ISENTROPIC ASCENT BRUSHING FAR SOUTHERN MICHIGAN FROM LATE
MORNING THROUGH EARLY EVENING. BETTER MOISTURE SHOULD REMAIN SOUTH
OF THE AREA...WITH 6-8C DEWPOINTS AT H850 NOT MAKING IT NORTH OF THE
LOWER PORTIONS OF THE FRONTAL SLOPE AND UP INTO MICHIGAN. H850
DEWPOINTS OVER SOUTHEAST MICHIGAN LOOK TO REMAIN BELOW FREEZING PER
LATEST MODEL SOLUTIONS...INCLUDING THE WETTER GFS. AVAILABLE
MOISTURE AND FORCING WILL FIRST NEED TO OVERCOME THE CURRENT DRY
AIRMASS TO GENERATE SHOWERS...AND THEN FIGHT THE INFLUENCE OF DRY
NORTHEAST FLOW OUT OF CANADA. AGREE WITH PREVIOUS FORECAST THAT GFS
SOLUTION IS OVERDONE WITH QPF...AND THAT THERE WILL BE A SHARP EDGE
TO THE PRECIPITATION SHIELD. KEPT POPS LIMITED TO M-59 SOUTH.
CONFIDENCE OVERALL WITH THE PRECIPITATION FORECAST IS NOT HIGH. ON
ONE HAND...MOISTURE AND FORCING DO NOT LOOK TERRIBLY FAVORABLE THIS
FAR NORTH. ON THE OTHER HAND...SHOWERS/TSTORMS ONGOING OVER
IOWA/MINNESOTA WILL NEED TO BE WATCHED TO SEE IF THEY CAN MANAGE TO
SURVIVE THE STABILIZING INFLUENCE OF UPPER RIDGING TONIGHT AND EARLY
TOMORROW...AND MANAGE TO TRACK EAST INTO THE AREA. IF PRECIP BEGINS
EARLY ENOUGH IN THE DAY WE COULD SEE A FEW WET SNOWFLAKES AT ONSET
BEFORE DIURNAL HEATING SETS IN. EAST TO NORTHEAST FLOW WILL KEEP
TEMPERATURES COOL...ESPECIALLY NEAR THE LAKESHORES. EXPECTING MAX
TEMPS IN THE LOW 50S FURTHER INLAND WITH 40S NEAR THE LAKES.

SHORTWAVE TROUGH OVER CANADA WILL CONTINUE TO DROP SOUTH THROUGH
MICHIGAN SUNDAY INTO SUNDAY NIGHT. THIS WILL REINFORCE NORTHERLY
FLOW OVER THE AREA...KEEPING TEMPERATURES BELOW NORMAL (IN THE 50S)
AND PARTICULARLY COOL NEAR THE LAKE HURON SHORELINE. GFS/NAM DO SHOW
A MODEST INCREASE IN MID/LOW-LEVEL MOISTURE ASSOCIATED WITH THE
PASSAGE OF THIS SHORTWAVE...MOSTLY ACROSS THE FAR EASTERN PORTION OF
MICHIGAN. AT THIS TIME...WILL KEEP THE FORECAST DRY AS THIS WAVE
WORKS ACROSS. MOISTURE ADVECTION DOES NOT LOOK TOO STRONG
CONSIDERING THE PRECEDING DRY AIRMASS.

FAIRLY QUIET EXTENDED PERIOD IS IN STORE FOR SOUTHEAST MICHIGAN.
HIGH PRESSURE BUILDS INTO THE AREA EARLY NEXT WEEK AND REMAINS OVER
THE REGION THROUGH THE END OF THE WEEK. THIS WILL KEEP CONDITIONS
DRY AND WILL RESULT IN A WARMING TREND THROUGH NEXT FRIDAY AS
SOUTHERLY WINDS FILTER IN A WARMER AIRMASS FROM THE SOUTH. RESULTING
HIGH TEMPS WILL REMAIN IN THE LOW TO MID 60S WITH OVERNIGHT LOW
TEMPS IN THE LOW TO MID 40S THROUGH FRIDAY.

MARINE...

A RIDGE OF HIGH PRESSURE OVER THE CENTRAL GREAT LAKES WILL BRING
FAIRLY LIGHT WINDS TONIGHT INTO EARLY SATURDAY. WINDS WILL THEN TURN
EAST TO NORTHEAST AND GUST TO 20 KNOTS BY SATURDAY AFTERNOON AS LOW
PRESSURE TRACKS THROUGH THE SOUTHERN OHIO VALLEY. WAVES WILL BUILD
OVER SAGINAW BAY DURING THE AFTERNOON AND EVENING...HOWEVER THEY
LOOK TO REMAIN AT 3 FEET OR LESS. SMALL CRAFT ADVISORIES COULD BE
NEEDED BY SATURDAY NIGHT OR SUNDAY AS PERSISTENT NORTH FLOW ALLOWS
WAVE HEIGHTS TO POTENTIALLY BUILD IN EXCESS OF 4 FEET OVER SOUTHERN
LAKE HURON.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...NONE.
LAKE ST CLAIR...NONE.
MICHIGAN WATERS OF LAKE ERIE...NONE.
&&

$$

AVIATION.....CB
SHORT TERM...SF
LONG TERM....HLO/RK
MARINE.......HLO


YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE
AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).



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